Steoboscopic testing apparatus



Dec. 21,- 1943. D. D. KNowLEs STROBOSCOPIC TESTINGv APPARA'US 2 sheets-sheet 1 l Original Filed Oct. 1, 1950 mvENToR en/qyJmWles BY l d Dec-.21, 1943. D D KNOWQES l I Re.22,40s

STROBOSCOPI C TES TING APPARATUS Orig-nal Filed Oct. l, 1930 2 Sheets-Sheet.. 2

INVENTOR A B-Y y ATTORN v Reissued Dec. 21, 1943 UNITED STATES l PATENT OFFICE 22,403 I l STROBOSCOPIVC TESTING APPARATUS Dewey D. Knowles. Verona, N.v J., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania original N0.'1,919,69z, dated November s, 1934,

Serial No. 485,809, October 1, 1930.

Application for reissue March Z4, 1941, Serial No.

by a beam of light is adapted to dash intermittently in accordance with the frequency of the rotating or vibrating object.

The theory of my invention is briefly described as follows:

supposing that an object has a periodic motion and that, at exactly the same point in the opposite cycle of motion, a. light of short duration is flashed upon it, then, to the eye or camera,

saidobject will be visible only Whenvthe light is upon it. As this period is of short duration and always occurs when the body is in exactly the same position, the result is that the object ap pears motionless. If` the frequency of the flash of light is made slightly less than the frequency of the periodic motion, the object will be seen at a different pointI during each successive cycle, and it will appear to be tracing its course at a frequency equal to the difference between its actual frequency and the frequency of the light flashes. Correspondingly, if the frequency of the light flashes is greater than that of the object studied, it will appear as if the object is tracing its course `in a reverse direction.

The object is visible during the entire period that the light is upon it, and, in order that the visibility be not blurred, the light must be of very short duration. It is necessary, therefore, that means of obtaining a light of considerable intensity and very short duration be provided.

An object of my invention, therefore, is to pro` flashing a light at a frequencyof the rotating Ys claims. (c1. 3154238) Fig. 2 is a View, in side elevation, partly in section, of one of the grid-glow tubes shown in Fig. 1;

Fig. 3 is a View, in side elevation, partly in v section, of a contactor deviceconstructed in accordance with my invention;

Fig. 4 is a view, in front elevation, of the device shown in Fig. 3, parts being broken away.

Referring to Figs. 1 and 2,V a three-lamp unit I comprises three grid-controlled electric-dis- -charge tubes` 2, 3 and 4. Since the tubes 2, 3 and 4 are of identical structure and have the same circuit connections, only the tube 2 will be described in detail. The tube 2 comprises a filament 5, an anode B and a grid The usual base member B is provided, through which the contact members 9 and I0 of the lament 5 and contact members II and I2 of the anode 6 and grid 1, respectively, protrude. A receptacle I3, adapted to receive the contact members 3,' I0, II and I2, is secured at one end of a hollow handle I4 which is constructed of insulating material. A shield or reflector |34 is secured to the handle I4 below the receptacle I3, and the reflector |34 is connected, by means of a conductor |35, to conductor I6 of the lament circuit to shield the tube from the body-capacity of the operator. A flexible cable I5 is secured at the other end of the handle I4 and is adapted to carry conductors I6 and I'I, which are connected, through the receptacle I3, to the contact members 9 and IU, and conductors I8 and I9 are connected, respectively, through. the receptacle I3, to contact members II and I2.

A connecting plug 20 of insulating material is secured to cable I5, at one end thereof, and is provided with male contactmembers 2l, 22, 23 and 24, which are connected, respectively, to conductors I6, I'I, I8 and I9.

A condenser 25, in thevhollow portion of the handle I4, is connected to conductors I6 and I8, and a resistor 26 is connected to conductors Il and I9 for a purpose to be hereinafter more fully explained. n

The unit I is provided with three socket members 2T, 28 and 29. Each of the socket members has female contact members 3|, 32, 33 and 34, adapted to receive, respectively, the male contact members 2|, 22, 23 and 24 of the connecting plug 20.

The hinge members of a four-pole doublethrow switch 35, are connected, through conductors 36 and 3l, to a source of electric energy (not shown). A primary winding 38 of a. transformer 39 is so connected to the jaw members of the switch 35'that current will flow through the primary winding 39when the switch 35 Ls Vin either of its closed positions. 'I'he ltransformer 39 has three secondary windings 40, 4| and 42. Each of the secondary windings 40, 4I and 42 are connected, respectively, through variable resis' torsl 43, 44 and 45, to the contact members 3| and 32 of the respective socket members 21, 29 and 29.

A primary winding 49 of a transformer 41 is so connected to the switch 35 that the winding 49 will become energized when the switch 35 is in its lower closed position. The transformer 41 also comprises a high-voltage secondary winding 49 and a low-voltage secondary winding 49.

A power pack 50, comprising a rectifying tube 5| condensers 52 and 53 and a choke coil 54, is

90, 9| and 92, respectively, to the contact member 33 of the socket members 21, 29 Aand 29, re-

` spectively.

The contactmembers 32 of the socket members i 2'1, 29 and 29 are connected,through conductor 93, to the variable point of resistor 59.

'I'he minus side of power pack` 50 is connected,`

ber |04 and resistor 55, to the negative side of the output of the power pack 50.

The Ynegative side of the output of the mltivibrator unit 91 is connected, through condenser |05, conductor |06 and female contact member |01, to the positive side of the output of the power pack 50.

'The examiningrotating objects secured to a shaft having a lathe center, the modification shown in Figs. Sand 4 may be used. Referring to Fig. 3, amechanical contacter |03 is illustrated. A hollow metal casing |09 is provided with a recess near one end in .which a ring I|0 of insulating materialis slidably mounted.

A shaft member is rotatably mounted, by means of bearing members ||2 and l|i 3, in the casing |09. The shaftis provided With a collar 4 and an adjustable nut ||5 to prevent longitudinal movement of the shaft with respect to the bearing members. One endof the shaft is adapted to protrude through an opening in the casing |09 and is fitted' with a tachometer tip ||9 having .a conical bearing surface |I1. A metal spider I9 yis fixedly secured `to the shaft and is adapted to rotate therewith. A steel Y edge of the spider 8 in such manner that the through resistor 55, and conductor 91', to contact members 34 of the socket members 21, 29 and' 29,- through resistors 94, 93 and 99, respectively.

A multi-vibrator unit 91 comprises a pair of vacuum tubes 93 and 99. f The tube 99 comprises a filament 10, plate 1|, cathode 12 and grid 13. The tube 99 comprises a filament 14, a plate 15, a cathode 19 and a grid 11.

A primary winding 19 of a transformer 19 is adapted to be energized through conductors 90 and 9| and a, switch 92 by a source of energy (not shown). i

A power pack 93. comprising a rectifylng tube 94, condensers 95, 99, 91 and choke coils 99 and 99, is energized by a high-voltage secondarywinding 90 and a low-voltage secondary winding 9| \of the transformer 19. A third secondary winding 92 of the transformer 19 serves to energize the filaments 10 and 14 of the tubes 99 and The cathodes 12 and 19 of-the respective tubes 69 and 99--are connected, through conductor 93 and a switch 94, to the negative side ofthe output of power pack 93.

The grids 13 and 11`of the respective tubes 99 and 69 are connected,` through a'variable resistor 95, to the circuit controlling the cathodes 12 and 15.

The plates y1| and 15 of the tubes 99 and 59, respectively, are connected, through fixed resistors 99 and 91, respectively, and a variable Lil kco

resistor 99, to the positive side of the output of power pack 93.

The grid member 13 of the tube 99- is connected, through a condenser 99, to plate 15 of the tube 99. The grid 11 ofthe tube 99 is connected, in like manner, through a condenser |00, to the plate 1|,of tube 99.

`A voltmeter |0| is connected from the plus side of the multivibrator unit to conductor 93 for a purpose tobe hereinafter more fully` explained.

i The positive side of the output of the ymultivibrator unit 911s connected, through a con-I `denser |02, conductor |03, female contact mem.

tip `protrudes therefrom. A contact member |22, having a conical tip |23is yieldingly mounted, by means of a collar |24 and a spring |25, in a recess provided in the insulated ring I0.

An arcuate slot |25 is .provided in the casing |09 through which protrudes a, threaded pin |21 which is secured tothe slidably mounted ring I0. A knurled nut is adapted to be screwed upon the pin |21 to prevent movement of the pin with respect tothe casing. The shaft is mounted eccentrically with respect to the axis'of the ring I0. It is apparent, therefore, that `adjustment of the contact member |22, with respect to the contact member ||9, may be made by shifting the position of the ring I0.

An insulated conductor |29 is connected to the contact member |22, and a conductor |29 is grounded to the casing |09 by means of a terminal member |30. Conductors |29 and |29 are connected, through a flexiblecable |3|, to male contact members |32 and |33, respectively.`

vThe operation of the device, when using the multivibrator unit, is as follows: The switch 35 is closed in its upperposition, and the filaments 5 of the tubes 2, 3 and 4 are energized. When the filaments are suciently heated, the switch 35 is actuated to its lower closed position. 'Ihe filaments 5 will still be energized,`and the power pack will be energized through transformer 41. The condensers 25 will then charge up to a high potential. The tubes will not break down, however, as the grids 1 are held at a, negative ,value with respect to the anodes 9 on account of resistor 29 andfresistors 94, 55 and 58. By varying the adjustment oi.' the variable resistor 59, the potential of the grids 1 may be adjusted to a value necessary for stable operation. If the potential of the grid is raised, the tube will break down,vcau sing the condenser y25 to discharge very rapidly, 'and cause the tubes to emit a bright flash of light of very short duration. The discharging of condenser 25 lowers the potential across the tubes to cause the breakdown to discontinue.

tact members |04 and |01, respectively, of the light unit I:

The trapezoidal wave form of the output of the multivibrator unit 61 impressed upon the condensers |02 and |05gives a very peaked current through the resistors 55 and 5B. The drop across the resistors 55 and 50 raises the potential of the grids 1, and the tubes 2, 3 and 4 will break down. Before the condenser 25 has again charged to a high value, the current from the multivibrator has dropped to zero. 'I'his cycle is continued in accordance with the frequency of the multivibrator.

Since the frequency ofthe multivibrator may be varied by adjusting the variable resistor l95, it is apparent that the frequency of the light flashes of tubes 2, land l may be varied Vat the will of the operator.

When a vibrating or rotating object is to be examined, the operator places the tubes 2, 3 and 4 so that their light is concentrated upon the object. The resistor 95 is then so adjusted that the frequency of the light flashes Vsynchronizes with the frequency of the object. The object will then appear to stand still. If it is desired -to study the progress of the object during a complete cycle, the frequency of the multivibrator may be slightly decreased, and the object being studied will appear to move slowly in a forward direction. In the same manner, if the frequency of the Amultivibrator is increased, the object will appear to move in a reverse direction.

The operation of the device, vwhen using the modification in Figs. 3 and 4, is as follows:

The switch 35 is actuated, as explained above, to rst heat the tube Ifilaments and then to es,- tablish a circuit through the power pack 50.

The male contact members |33 and |32 are connected to the female contact members |01 and |04, respectively. The operator then grasps the handle |09 of the mechanical contacter |08 and places the tip in operative contact with the lathe center of a rotating object. The metal spider ||'8 Will ,then revolve at exactly the same speed as the rotating object, and the tips |20 .and |23 of the contact members ||9 and |22,

respectively, will engage once for every revolution l of the object. During the period of contact, the grid 1 will be momentarily connected, thrigh resistor 64 to the anode 0, and a relatively high potential will beimpressed upon the grids 1 of the tubes 2, 3 and I. As explained above, the tubes will then break down, condensers 25 will discharge, and the tubes will emit a brilliant flash of light. Before the next contact, the condensers will recharge, and the same operation will thus take place for every revolution ofthe mechanical contacter.

The conical tips of the contact `members ||'9 and |22 are made of polished steel and are so constructed that a minimum of arcing takes place when contact is broken.

`I do not Wish to be restricted to the specific arrangement of parts and circuit connections shown and described as it is evident that various modifications thereof will fall within the spirit and scope of my invention. I desire, therefore, that only such limitations be imposed as are indicated in the appended claims.

I claim as my invention:

1. A contactor device for dashing a strobosco'pe in synchronism with a rotating member comprisihg a casing, a ring rotatably mounted within said casing, a contact member secured to said ring, a shaft eccentrically mounted with respect to said ring within said casing, a spider secured to said shaft, a second contact member secured to said spider, means associated with said ring for adjusting the position of said first mentioned contact lmember with respect to said second contact member, and friction driving means on said shaft forengaging the rotating member.

2. Electrical apparatus comprising a grid-glow tube having a cathode, an anode, and a control electrode, means for applying a voltage across said cathode and said anode, and means for periodically applying a voltage to said control electrode of sufficient value to 'cause a discharge in said tube, said last means comprising a multivibrator with an output voltage of a'tapezoidal wave form.

3. Electrical apparatus comprising a grid-glow tube having a cathode, an anode, and a control electrode, means for applying a voltage across said cathode and said anode, a condenser connected across said cathode and said anode, and means for periodically applying a voltage to said control electrode of sufficient value to cause a discharge in said tube, said last means comprising a multivibrator with an output voltage of a trapezoidal wave form.

4. A stroboscope for viewing an object in motion comprising a light source in the light from which said object may be viewed, means including a source of direct current and a voltage operated device for causing said light source to emit a flash of light in response to a voltage abovev a predetermined value applied to said device, and means Afor periodically applying a voltage having a substantially vertical wave front to said voltage operated device, the maximum value of the voltage at the Wave front being greater than said predetermined value. 5. Electrical apparatus comprising a grid-glow tube having a cathode, an anode, and a controlv electrode, a condenser connected across said cathode vand said anode, means for applying a periodic voltage of trapezoidal wave form to said control electrode, and means for charging said condenser, the charging rate being such that said periodic voltage has dropped to zero before said condenser becomes fully charged.

6. Electrical apparatus comprising an electrical tube of the gas filled type having a cathode, an

' l predetermined voltage.- A

control electrode, a condenser conand said anode, lsaid anode, and a nected across said cathode tube having the characteristic that with a predetermined charge on said condenser and a predetermined voltage on said control electrode a discharge will take place between said cathode and said anode, means for applying to said control electrode a periodic voltage having a steep wave front and having a maximum voltage at least equal to said predetermined voltage, and means for charging said condenser; the charging rate beingfsuch that said condenser does not reach said predetermined charge until said periodic voltage has decreased to a value below said DEWEY D. nNowLEs. 

